The Social Life of Subatomic Particles

The various materials that we experience in everyday life are built from molecules. In turn, molecules are built from atoms. Atoms are built from electrons and nuclei. Nuclei are built from protons and neutrons, which were once considered “elementary particles”. Bob Hofstadter won his Nobel Prize for dispelling this notion by showing that protons have an internal structure and measuring their size. I will describe how, building on his work, we learned that protons and neutrons are built from particles called quarks and gluons. As far as we know, this is where the “cosmic onion” ends. However, we have also discovered that quarks come in six different flavors and that they have a rich “social life”: they are never alone and always appear in clusters that correspond to protons, neutrons and their numerous cousins. In recent years experiments in giant particle accelerators have dramatically advanced our understanding of the "social preferences" of quarks, revealing many exotic clusters and determining which ones are stable enough to be observed experimentally and how quarks are arranged inside them.

Speaker: Marek Karliner, Tel Aviv University, emeritus